1. Field of the Invention
The invention relates to a vibration generator with adjustable eccentric weight having a driven excitation shaft with which there rotates at least one first eccentric weight together with a second eccentric weight which can be adjusted by turning.
2. Description of the Prior Art
Such vibration generators are typically used in conveyors or in ramming tools together with sorting, distribution, metering, compacting, loosening or mixing machines, e.g. in ramming tools, vibratory conveyors, vibratory sieves, vibrating tables etc. For the different applications it is necessary to match the vibration frequency, the vibration amplitude and particularly the excitation force to the individual demands. For this purpose, to adjust the frequency of speed of rotation of the eccentric weights can be altered. The vibration amplitude can be affected by the static torque of the eccentric weights and by alteration of the centrifugal force of the rotary weights the excitation force can be brought to the desired value, for example by adjustment of the eccentricity or by adjustment of the relative phase position of the weights which are fixed to and adjustable on the excitation shaft. If the individual parameters to match the mechanism to the operating conditions are only adjusted when stationary this causes inconvenient interruptions in operation. Apart from this in most cases precise and economical setting of the mechanism can only be effected during operation since because of the quadratic relationship of the excitation force to the rate of vibration a larger number of adjustments will be necessary when stationary, resulting in uneconomic interruptions of work.
A method is known whereby vibration generators with several eccentric weight shafts can have these eccentric shafts turned to vary their relative phase position, thus increasing or reducing the vibration amplitude by vectorial addition or subtraction. Adjustment of the phase position is effected by means of drives, for example epicyclic, bevel gear, differential or worm drives which are expensive to produce and generally do not allow compact construction of a machine. Such complicated drives are also currently to be found on vibration generators having only a single eccentric shaft where there are eccentric weights fixed to and adjustable on the shaft, the relative angle between the two weights, whose eccentricity is generally equal, being variable by these drives. Thus the resulting vibration amplitude can be varied from zero, where the eccentric weights cancel each other out when situated in diametrically opposite positions in relation to the axis of rotation, to a maximum where they are axially in line. Particularly with existing vibration generators with a single eccentric weight shaft and where it is desired to achieve a compact design with easy to handle means to adjust the eccentric weights, the drives as described above generally occupy an appreciable space where costs have had to be kept down.
In order to reduce the complication in the drive for adjusting the relative angle between the eccentric weights a method is known whereby the excitation force of the vibration generator is adjusted dependent on speed, using the centrifugal force of the eccentric weights during operation. (German Patent O.S. No. 25 53 800). With this design the excitation shaft has a portion eccentric to its axis on which the adjustable eccentric weight is mounted with a spring inserted between the fixed weight and the adjustable one acting in the peripheral direction, and acting in opposition to the centrifugal force of the adjustable eccentric weight while running and when not locked so that as the speed is altered angular adjustment can be effected between the two weights. After setting of an angle, locking devices to hold the adjustable weight in position on the excitation shaft are actuated. Although this existing vibration mechanism has essential advantages as regards other known ones as regards its robust and compact construction, reliability and simple and rapid possiblity of adjustment, adjustment of the excitation force which is only possible while working is in many cases found inconvenient.